The invention relates to a cleaning apparatus that is comprised of (1) a pressure tank with at least one cleaning tank arranged therein, in which the cleaning is performed, and (2) means for supplying the cleaning apparatus with a cleaning fluid. In addition, the cleaning tank or tanks are movably arranged in relation to the pressure tank.
The invention further relates to a method for cleaning substrates using liquefied and/or supercritical gases as cleaning fluid in at least one cleaning tank, which is arranged inside a pressure tank. The cleaning tank or tanks is/are moved at least for part of the time during the cleaning process in relation to the pressure tank.
Cleaning devices of this type, which are used, for example, for cleaning processes involving liquid or supercritical carbon dioxide but that may also be used as cleaning fluid in connection with any other materials or components, are generally designed for use with operating pressures of higher than 60 bar. To improve the cleaning result, it is necessary to generate a relative movement between the material being cleaned and the cleaning fluid. This relative movement can be created by using suitable nozzle systems which move the material that is being cleaned around in a cleaning cylinder, while the cleaning cylinder itself is not being moved.
Also known in the art is a process that puts the cleaning cylinder itself in a rotation in order to positively influence the cleaning result by way of the dropping-down [motion] of the material being cleaned. The rotational movement of the cleaning cylinder can be executed in alternating directions of rotation and/or speed of rotation.
If the cleaning system or the cleaning tank is intended to be used for cleaning processes that take place under high pressure, the cleaning cylinder, that is arranged inside the pressure container or the pressure cleaning tank, is driven via an axle or shaft that penetrates through the pressure container, such as is disclosed, for example, in DE-A 42 30 485. However, this configuration requires costly sealing and/or packing systems, because the drive motor is located outside of the pressure tank.
Recent findings have shown that the cleaning efficiency, especially of carbon dioxide, can be improved with higher operating pressures: under consideration are operating pressures of more than 200 bar. But sealing the shaft lead-through becomes more difficult and energy intensive with increasing pressure. Due to the wall thickness of the pressure container, that is necessary for these high pressure levels, it is not possible to realize contact-free transmission via a magnetic coupling.
Known in the art is, for example from WO-A 94/01613 (U.S. Pat. No. 5,267,455), a drive by way of the rotation of a cleaning cylinder, which is magnetically connected with a drive motor, for the cleaning of substrates using liquefied and/or supercritical gases as the cleaning fluid.
However, regardless of the selected pressure level for the cleaning process in the cleaning tank, disadvantages can result if the cleaning cylinder is driven via a magnetic coupling, because the magnetic field influences the cleaning; e.g. by way of contamination that is present in the cleaning fluid and can become concentrated in certain areas of the cleaning tank as a result of the magnetic field.
Therefore, it is the subject-matter of the present invention to describe an apparatus and a method of the type described at the outset that will avoid the above-mentioned disadvantages and provide an improved cleaning system for cleaning at different pressure levels. In particular, moving axles or shafts designed to drive the cleaning tank, penetrating through the pressure tank, are to be eliminated. To be described is an alternative for generating the movement of the cleaning tank using a magnetic coupling.
For the apparatus, this objective is achieved according to the invention by envisioning that the means for setting the cleaning tank in rotational and/or translational motion relative to the pressure tank comprise a hydraulic motor located inside the pressure tank.
For the method, this objective is achieved according to the invention by envisioning that the cleaning tank or tanks is or are set in rotational and/or translational motion relative to the pressure tank via the means located inside the pressure tank for setting the cleaning tank or tanks in motion, without movable shafts that would penetrate the pressure tank, and/or without a magnetic coupling of the cleaning tank.
The invention is based upon the idea of eliminating, on the one hand, the magnetic coupling between the cleaning tank and the drive mechanism, because of the above-described disadvantages, and, on the other hand, on arranging the means for setting the cleaning tank in motion inside the pressure tank in order to avoid the use of movable shafts (rotating shafts) that are costly to seal and penetrate through the pressure tank. To this end, the drive means are positioned inside the pressure tank and, simultaneously, inside and/or preferably outside the cleaning tank.
The means for setting the cleaning tank in motion may include any and all suitable drive mechanisms, such as hydraulic motors or electric motors, or nozzles combined with an impeller wheel. If hydraulic motors are used, additional advantages can result, provided the cleaning fluid is also used as drive medium for the motor.
As a result, in the context of the invention, there may only be non-moving feed-throughs, e.g. feed-throughs for hydraulic fluid if a hydraulic motor is used as the drive mechanism for the cleaning tank, electrical lines if an electric motor is used as the drive mechanism for the cleaning tank, or one or more nozzles directed at an impeller wheel.
The cleaning tank can, for example, be designed as a cleaning cylinder or a cleaning basket.
In a further embodiment of the invention, the at least one supply line for filling the tank with cleaning fluid and/or for emptying the tank can be disconnected before the cleaning tank is set in motion, or it can be wound up while the cleaning tank is moving.
It is noted that if the cleaning device specified in the invention is used in cleaning processes that are not implemented under pressure, the containers obviously do not need to be pressure-tight. This type of embodiment of the cleaning device is implied in the context of the invention. However, cleaning processes that use a cleaning fluid comprising liquefied and/or, above all, supercritical gases, cannot be implemented without pressure.
Contrary to the known state of the art, which provided for the generation of movement of the cleaning tank by way of a magnetic coupling, it is now possible to eliminate the rotary lead-throughs passing through the pressure container for the cleaning tank that were necessary until now. According to the invention, the cleaning tank, which is arranged inside the pressure tank, is now set in motion, and preferably it is rotated. This results in a relative movement between the material being cleaned (substrate) and the cleaning fluid, leading to the desired improvement of the cleaning effect.
Suitable cleaning fluids according to the invention include especially all known liquefiable gases, such as carbon dioxide, dinitrogen monoxide, sulphur hexafluoride, or hydrocarbons, such as methane, ethane, propane, ethene, propene etc., as well as halogenated hydrocarbons, such as trifluoromethane and mixtures of the above-named substances.
With regard to the invention, carbon dioxide has proven to be a particularly well suited fluid because it has certain advantages. Carbon dioxide is non-flammable, non-explosive and large quantities of it are available at low cost since it is an industrial by-product. In comparison to other solvents, carbon dioxide has only a minimal environmental impact, and carbon dioxide is chemically inert. Furthermore, its thermodynamic properties make carbon dioxide a good candidate for use as a cleaning agent.
Preferably, the cleaning process is implemented using liquefied (sub-critical) carbon dioxide. This applies especially for the cleaning of textiles, carpets and the like.
According to the invention, the cleaning process can be performed at all suitable pressures (even above 200 bar) and temperatures.
Advantageously, the cleaning process is implemented at a pressure of less than 100 bar, preferably at between 25 and 80 bar, and most preferably at a pressure of between 30 and 70 bar.
Advantageously, the cleaning process is implemented at a temperature of between xe2x88x9220xc2x0 C. and +40xc2x0 C., preferably at a temperature of between xe2x88x9215xc2x0 C. and +25xc2x0 C., and most preferably at a temperature of between 0 and +15xc2x0 C.
Good cleaning results with liquefied carbon dioxide were achieved, for example, at a pressure of between 25 and 75 bar and at a temperature of between xe2x88x9215 and +25xc2x0 C., in particular at a pressure of between 40 and 50 bar and at a temperature of between +5xc2x0 C. and +10xc2x0 C.
Particular advantages with regard to cleaning fluid consumption, and therefore the cost-effectiveness of the cleaning process, result from the fact that the liquefied gas is at least partially re-circulated. Suitable means to accomplish this can be present as part of the cleaning system.
In a favorable embodiment of the cleaning process according to the invention, cleaning intensifiers, such as chemical solvents, are added to the cleaning fluid. Chemical solvents, such as e.g. surface-active agents, HCl, alcohols, anhydrous soaps etc., increase the solvency effectiveness of the liquefied gas used as cleaning fluid.
Adding mechanical scouring agents, such as plastic granulate, steel scrap or slag sand, is also conceivable in order to effect an additional mechanical removal of the surface layers of the substance that is to be dissolved.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.